1. Field of the Invention
The present invention relates to an image processing apparatus which processes an image, an image forming apparatus, an image processing method, and a computer-readable recording medium on which an image processing program is recorded.
2. Description of the Related Art
Among image forming apparatuses such as a digital color copying machine and a multifunction peripheral, some image forming apparatuses have a two-color mode for outputting a two-color image besides a full-color mode for outputting a full-color image and a monochrome mode for outputting a monochrome image.
In the two-color mode, the image forming apparatus outputs all chromatic colors in an original document or a chromatic color (e.g., red), which an operator (user) designates in advance by extracting the chromatic color from the original document, in the chromatic color (e.g., red) designated by the user in advance and outputs portions of other colors in the original document in an achromatic color (black). Consequently, the image forming apparatus can obtain, while reducing a usage of color materials to be smaller than that in the full-color mode, an output image having better color expression than that in the monochrome mode.
In the two-color mode, an image processing apparatus performs a two color process for converting an image of a full-color original document into a two-color image of color composition different from the image. Therefore, it is difficult for the user to surmise whether a two-color image of assumed color composition can be obtained. The user can check, by performing trial printing, color composition of a two-color image to be obtained in the two-color mode. However, as explained above, the two-color mode has a main purpose of reducing a usage of color materials to be smaller than that in the full-color mode. Therefore, it is desirable that the trial printing is unnecessary.
To solve such a problem, Japanese Unexamined Patent Publication JP-A 2006-270222 discloses an image processing apparatus configured to be capable of displaying an image outputted in the two-color mode on an image display device before actually outputting the image. With the image processing apparatus disclosed in JP-A 2006-270222, the user can visually check the image outputted in the two-color mode in the image displayed on the image display device before actually outputting the image.
However, as in the image processing apparatus disclosed in JP-A 2006-270222, in a two color process for converting input image data of RGB (R: red, G: green, G: blue) inputted by reading an original image into image data of CMYK (C: cyan, M: magenta, Y: yellow, K: black) for outputting a two-color image formed of two colors of a chromatic color and an achromatic color, in some case, an amount of color materials used in outputting the two-color image increases to be larger than an amount of color materials used in outputting a full-color image.
For example, in processing for converting input image data of RGB inputted by reading an original document into image data of CMYK for outputting a full-color image, when a two color process for output in red designated by the user is applied to a pixel, density (pixel) values of planes of C, M, Y, and K of which are converted into (C, M, Y, K)=(255, 0, 0, 0), density values of the planes of C, M, Y, and K in image data after the conversion are (C, M, Y, K)=(0, 255, 255, 0).
In this way, whereas color materials equivalent to C=255 are used when the full-color image is outputted, color materials equivalent to 510 as a total of M=255 and Y=255 are used when the two-color image is outputted.
Specifically, in the image processing apparatus disclosed in JP-A 2006-270222, the user can visually check a two-color image in an image displayed on the image display device before actually outputting the two-color image and check whether a desired two color process is applied in terms of image quality. However, the user cannot check whether a desired two color process is applied in terms of a usage of color materials.